Dear Varge,
Good day! Thank you for posting your query in our community.
Based on your description, you want to unhide column in Project for the web.
You can check my test image(the Test field is a custom field and I hide it. If you want to unhide it, you can choose it in the Add column list):
If my understanding is wrong, please feel free to post back.
Sincerely,
Jazlyn | Microsoft Community Moderator